Methods, systems, and computer readable media for network slice selection function recovery

ABSTRACT

Methods, systems, and computer readable media for network slice selection function (NSSF) recovery. A method includes creating, at an NSSF, subscriptions for a number of access and mobility management functions (AMFs) and storing availability information for each AMF. The method includes determining, at the NSSF, that the NSSF failed to process at least one service update message from at least one of the AMFs, and in response, sending a notification request message to each of the AMFs, the notification request message requesting each AMF to update availability information for the AMF. The method includes receiving, at the NSSF, updated availability information from each of the AMFs. The method includes distributing, at the NSSF, the updated availability information to each of the AMFs.

TECHNICAL FIELD

The subject matter described herein relates to telecommunicationsnetworks. More particularly, the subject matter described herein relatesto methods, systems, and computer readable media for network sliceselection function (NSSF) recovery.

BACKGROUND

In fifth generation (5G) communications networks, the network node thatprovides service is referred to as a producer network function (NF). Anetwork node that consumes services is referred to as a consumer NF. Anetwork function can be both a producer NF and a consumer NF dependingon whether it is consuming or providing service.

A given producer NF may have many service endpoints, where a serviceendpoint is the point of contact for one or more NF instances hosted bythe producer NF. The service endpoint is identified by a combination ofInternet protocol (IP) address and port number or a fully qualifieddomain name that resolves to an IP address and port number on a networknode that hosts a producer NF. An NF instance is an instance of aproducer NF that provides a service. A given producer NF may includemore than one NF instance. It should also be noted that multiple NFinstances can share the same service endpoint.

Producer NFs register with a network function repository function (NRF).The NRF maintains service profiles of available NF instances identifyingthe services supported by each NF instance. Consumer NFs can subscribeto receive information about producer NF instances that have registeredwith the NRF.

A network slice selection function (NSSF) provides network slicingservices for devices seeking to access specific network capabilities andcharacteristics associated with a network slice. An access and mobilitymanagement function (AMF) performs mobility management operationssimilar to those performed by a mobility management entity (MME) in 4Gnetworks. AMFs can subscribe to updates from the NSSF; however, thesubscribed AMFs may not receive these updates if the NSSF fails toprocess some update messages.

In light of these and other difficulties, there exists a need formethods, systems, and computer readable media for NSSF recovery.

SUMMARY

Methods, systems, and computer readable media for NSSF recovery. Amethod includes creating, at an NSSF, subscriptions for a number ofaccess and mobility management functions (AMFs) and storing availabilityinformation for each AMF. The method includes determining, at the NSSF,that the NSSF failed to process at least one service update message fromat least one of the AMFs, and in response, sending a notificationrequest message to each of the AMFs, the notification request messagerequesting each AMF to update availability information for the AMF. Themethod includes receiving, at the NSSF, updated availability informationfrom each of the AMFs. The method includes distributing, at the NSSF,the updated availability information to each of the AMFs.

According to another aspect of the subject matter described herein, theavailability information comprises network slice selection assistanceinformation.

According to another aspect of the subject matter described herein,determining that the NSSF failed to process at least one service updatemessage comprises determining that the NSSF implemented a trafficshedding policy in response to detecting an overload condition.

According to another aspect of the subject matter described herein,determining that the NSSF failed to process at least one service updatemessage comprises determining that the NSSF was unavailable for a periodof time.

According to another aspect of the subject matter described herein,creating the plurality of subscriptions comprises receiving a subscribeservice operation request message from each AMF.

According to another aspect of the subject matter described herein,storing availability information for each AMF comprises receiving anetwork slice selection assistance information (NSSAI) availability PUTrequest from each AMF.

According to another aspect of the subject matter described herein, themethod includes, after creating the plurality of subscriptions,receiving a network slice selection assistance information (NSSAI)availability PATCH request from at least one AMF and storing newavailability information for the at least one AMF.

According to another aspect of the subject matter described herein, themethod includes, after creating the plurality of subscriptions,receiving a network slice selection assistance information (NSSAI)availability update resulting from a telecommunications network operatorconfiguration and distributing the NSSAI availability update to each ofthe AMFs.

According to another aspect of the subject matter described herein,sending the notification request message to each of the AMFs comprisesincluding data requesting updated availability information in the formof a header or data attribute of a notify service operation message.

According to another aspect of the subject matter described herein, asystem for network slice selection function (NSSF) recovery includes atleast one processor and memory storing instruction for the at least oneprocessor. The system includes a NSSF implemented by the at least oneprocessor and configured for: creating subscriptions for a number ofaccess and mobility management functions (AMFs) and storing availabilityinformation for each AMF; determining that the NSSF failed to process atleast one service update message from at least one of the AMFs, and inresponse, sending a notification request message to each of the AMFs,the notification request message requesting each AMF to updateavailability information for the AMF; receiving updated availabilityinformation from each of the AMFs; and distributing the updatedavailability information to each of the AMFs.

According to another aspect of the subject matter described herein, theavailability information comprises network slice selection assistanceinformation.

According to another aspect of the subject matter described herein,determining that the NSSF failed to process at least one service updatemessage comprises determining that the NSSF implemented a trafficshedding policy in response to detecting an overload condition.

According to another aspect of the subject matter described herein,determining that the NSSF failed to process at least one service updatemessage comprises determining that the NSSF was unavailable for a periodof time.

According to another aspect of the subject matter described herein,creating the plurality of subscriptions comprises receiving a subscribeservice operation request message from each AMF.

According to another aspect of the subject matter described herein,storing availability information for each AMF comprises receiving anetwork slice selection assistance information (NSSAI) availability PUTrequest from each AMF.

According to another aspect of the subject matter described herein, theNSSF is configured for, after creating the plurality of subscriptions,receiving a network slice selection assistance information (NSSAI)availability PATCH request from at least one AMF and storing newavailability information for the at least one AMF.

According to another aspect of the subject matter described herein, theNSSF is configured for, after creating the plurality of subscriptions,receiving a network slice selection assistance information (NSSAI)availability update resulting from a telecommunications network operatorconfiguration and distributing the NSSAI availability update to each ofthe AMFs.

According to another aspect of the subject matter described herein,sending the notification request message to each of the AMFs comprisesincluding data requesting updated availability information in the formof a header or data attribute of a notify service operation message.

According to another aspect of the subject matter described herein, oneor more non-transitory computer readable media have stored thereonexecutable instructions that when executed by at least one processor ofa computer cause the computer to perform steps comprising creating, atan NSSF, a plurality of subscriptions for a plurality of access andmobility management functions (AMFs) and storing availabilityinformation for each AMF; determining, at the NSSF, that the NSSF failedto process at least one service update message from at least one of theAMFs, and in response, sending a notification request message to each ofthe AMFs, the notification request message requesting each AMF to updateavailability information for the AMF; receiving, at the NSSF, updatedavailability information from each of the AMFs; and distributing, at theNSSF, the updated availability information to each of the AMFs.

The subject matter described herein can be implemented in software incombination with hardware and/or firmware. For example, the subjectmatter described herein can be implemented in software executed by aprocessor. In one example implementation, the subject matter describedherein may be implemented using a computer readable medium having storedthereon computer executable instructions that when executed by theprocessor of a computer control the computer to perform steps.

Example computer readable media suitable for implementing the subjectmatter described herein include non-transitory devices, such as diskmemory devices, chip memory devices, programmable logic devices, andapplication specific integrated circuits. In addition, a computerreadable medium that implements the subject matter described herein maybe located on a single device or computing platform or may bedistributed across multiple devices or computing platforms.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter described herein will now be explained with referenceto the accompanying drawings of which:

FIG. 1 is a block diagram illustrating an example 5G system networkarchitecture;

FIG. 2 is a block diagram showing an example deployment of a NSSF andmultiple AMFs;

FIG. 3 is a ladder diagram illustrating an exchange of messages betweenan example NSSF, a first AMF, and a second AMF;

FIG. 4 is a table illustrating example attribute names and values for anotification message;

FIG. 5 is a ladder diagram showing an example exchange of messagesbetween an example NSSF, a first AMF, and a second AMF; and

FIG. 6 is a flow diagram of an example method for NSSF recovery.

DETAILED DESCRIPTION

The subject matter described herein relates to methods, systems, andcomputer readable media for network slice selection function (NSSF)recovery.

During deployments of telecommunications networks, typically multipleaccess and mobility management functions (AMFs) are deployed andconfigured to receive service from an NSSF. For example, each AMF cansend its network slice selection availability information (NSSAI) theNSSF using 3GPP defined operations. Other AMFs can subscribe for theNSSAI availability updates, e.g., updates due to updates from other AMFsor through telecommunications network operator configuration.

In some cases, the NSSF may go out of service due to any of variousreasons, for example, process crash, overload, database connectivityfailures or any other similar situations where the NSSF is unable toprocess the incoming NSSAI availability update requests coming from theAMFs. When the NSSF goes out of service, there could be multiple updatesthat will be missed to be applied on the NSSF storage on the NSSAIavailability information and eventually also missed to notify other AMFson the NSSAI availability update.

When the NSSF recovers from these failures, then there will be adiscrepancy between the NSSAI availability information among multipleAMFs (an AMF that updated the NSSAI and some other AMF that is expectingthe update notification) and between AMFs and the NSSF. With the staledata at the NSSF and AMFs, there is a possibility of a service outage.There is no 3GPP defined mechanism at the NSSF to request AMFs to resendthe updated data during the duration when NSSF was out of service.

This document describes a solution where, upon NSSF recovery from anyfailure scenarios, the NSSF can trigger a notification request towardsthe AMF for the valid subscriptions at NSSF. In the notificationrequest, the NSSF includes a new optional indication. Upon receiving thenotification trigger with optional indication, an AMF can trigger anNSSAI availability request towards the NSSF with the updated NSSAIavailability information. The NSSF can then process the request byupdating the storage and trigger a notification to all the subscribedAMFs.

FIG. 1 is a block diagram illustrating an example 5G system networkarchitecture. The architecture in FIG. 1 includes NRF 100 and SCP 101,which may be located in the same home public land mobile network(HPLMN). NRF 100 may maintain profiles of available producer NF serviceinstances and their supported services and allow consumer NFs or SCPs tosubscribe to and be notified of the registration of new/updated producerNF service instances.

SCP 101 may also support service discovery and selection of producer NFinstances. SCP 101 may perform load balancing of connections betweenconsumer and producer NFs. In addition, using the methodologiesdescribed herein, SCP 101 may perform preferred NF location basedselection and routing.

NRF 100 is a repository for NF or service profiles of producer NFinstances. In order to communicate with a producer NF instance, aconsumer NF or an SCP must obtain the NF or service profile or theproducer NF instance from NRF 100. The NF or service profile can be aJavaScript object notation (JSON) data structure as defined in 3GPPTechnical Specification (TS) 29.510.

In FIG. 1 , any of the nodes (other than NRF 100) can be either consumerNFs or producer NFs, depending on whether they are requesting orproviding services. In the illustrated example, the nodes include apolicy control function (PCF) 102 that performs policy relatedoperations in a network, a user data management (UDM) function 104 thatmanages user data, and an application function (AF) 106 that providesapplication services.

The nodes illustrated in FIG. 1 further include a session managementfunction (SMF) 108 that manages sessions between access and mobilitymanagement function (AMF) 110 and PCF 102. An authentication serverfunction (AUSF) 112 performs authentication services for user equipment(UEs), such as user equipment (UE) 114, seeking access to the network.

AMF 110 performs mobility management operations similar to thoseperformed by a mobility management entity (MME) in 4G networks. AMF 110can perform, e.g., registration management, reachability management,connection management, and mobility management.

A network exposure function (NEF) 118 provides application programminginterfaces (APIs) for application functions seeking to obtaininformation about Internet of things (IoT) devices and other UEsattached to the network. NEF 118 performs similar functions to theservice capability exposure function (SCEF) in 4G networks.

A radio access network (RAN) 120 connects user equipment (UE) 114 to thenetwork via a wireless link. Radio access network 120 may be accessedusing a g-Node B (gNB) (not shown in FIG. 1 ) or other wireless accesspoint. A user plane function (UPF) 122 can support various proxyfunctionality for user plane services. One example of such proxyfunctionality is multipath transmission control protocol (MPTCP) proxyfunctionality.

UPF 122 may also support performance measurement functionality, whichmay be used by UE 114 to obtain network performance measurements. Alsoillustrated in FIG. 1 is a data network (DN) 124 through which UEsaccess data network services, such as Internet services.

SEPP 126 filters incoming traffic from another PLMN and performstopology hiding for traffic exiting the home PLMN. SEPP 126 maycommunicate with an SEPP in a visitor PLMN which manages security forthe visitor PLMN. Thus, traffic between NFs in different PLMNs maytraverse two SEPP functions, one for the home PLMN and the other for thevisitor PLMN.

A network slice selection function (NSSF) 116 provides network slicingservices for devices seeking to access specific network capabilities andcharacteristics associated with a network slice. Network slices enablesusers to select customized networks with different functionality (e.g.,mobility) and/or performance requirements (e.g., latency, availability,reliability). Network slices may differ for supported features andnetwork function optimizations. In such cases, network slices may havedifferent S-NSSAIs with different slice and service types. The user candeploy instances of multiple network slices delivering exactly the samefeatures but for different groups of UEs. As these instances deliver adifferent committed service because they are dedicated to a customer, inwhich case such network slices may have different S-NSSAIs with the sameslice or service type but different slice differentiators.

NSSF 116 can support one or more of the following functionalities:

-   -   NSSF 116 enables AMF 110 to perform initial registration and PDU        session establishment.    -   NSSF 116 uses AMF 110 to update the S-NSSAI(s) the AMF supports        and notify any change in status.    -   NSSF 116 selects the network slicing instance (NSI) and        determines the authorized Network Slice Selection Assistance        Information (NSSAIs) and AMF 110 to serve the UE.    -   NSSF 116 interaction with NRF 100 allows retrieving specific NF        services to be used for registration request.

NSSF 116 can be responsible for providing the following information asand when queried by AMF 110:

-   -   Allowed NSSAIs    -   Configured NSSAIs    -   Restricted NSSAIs    -   Candidate AMF List (in case of registration)    -   Network Slice instance ID (for PDU registration)    -   Slice-level NRF information (for PDU Connectivity)

NSSF 116 can support the above functions through the following NSSFservices:

-   -   Network Slice Selection service (Nnssf_NSSelection): This        service is used by an NF Service Consumer (AMF) to retrieve the        information related to network slice. Network Slice Selection        Service enables Network Slice selection in the serving Home        Public Land Mobile Network (HPLMN).    -   NS-Availability Service (Nnssf_NSAvailability): This service is        used by an NF Service Consumer (AMF) to update the S-NSSAI(s)        the AMF supports on a per TA basis on the NSSF. Also, to notify        any change in status, on a per TA basis, of the SNSSAIs        available per TA (unrestricted) and the restricted SNSSAI(s) per        PLMN in that TA in the serving PLMN of the UE.

NSSF 116 can be configured such that, upon recovery from any failurescenarios, NSSF 116 can trigger a notification request towardssubscribed AMFs. In the notification request, NSSF 116 includes a newoptional indication. Upon receiving the notification trigger withoptional indication, an AMF can trigger an NSSAI availability requesttowards NSSF 116 with the updated NSSAI availability information. NSSF116 can then process the request by updating the storage and trigger anotification to all the subscribed AMFs.

FIG. 2 is a block diagram showing an example deployment 200 of a NSSF202 and multiple AMFs 204, 206, and 208. Each of AMFs 204, 206, and 208is configured to send NSSAI availability information to NSSF 202, forexample, as described in 3GPP Technical Specification TS 29.531. Each ofAMFs 204, 206, and 208 subscribes to NSSF 202 for the NSSAI availabilityupdates reported by other AMFs.

The NSSAI availability information can be updated due to, for example,updates coming from AMFs as well as through operator defined policyconfigurations. At NSSF 202, the NSSAI availability information isstored persistently to avoid losing data in case NSSF 202 experiences afailure. The NSSAI availability information can be stored, for example,in a database 210.

3GPP technical specification 29.531 section 5.3 states that theNnssf_NSSAIAvailability service is used by the NF service consumer(e.g., AMF) to update the S-NSSAI(s) the AMF supports on a per TA basisto NSSF 202, subscribe and unsubscribe the notification of any changesto the NSSAI availability information on a per TA basis, of the S-NSSAIsavailable per TA (unrestricted) and the restricted S-NSSAI(s) per PLMNin that TA in the serving PLMN of the UE.

For the Nnssf_NSSAIAvailability service the following service operationsare defined:

-   -   1. Update    -   2. Subscribe    -   3. Unsubscribe    -   4. Notify    -   5. Delete    -   6. Options

3GPP technical specification 29.531 section 5.3.2.2 explains the updateservice operation used by an NF Service Consumer (e.g., AMF) to updateNSSF 202 with the S-NSSAIs the NF service consumer (e.g. AMF) supportsper TA, and get the availability of the S-NSSAIs per TA for the S-NSSAIsthe NF service consumer (e.g. AMF) supports. The service consumer (AMF)shall send the NSSAI availability information to NSSF 202. NSSF 202stores this data for other AMF to use during registration and PDUestablishment. In brief, NSSAI availability information is state dataupdated by the AMF and stored at NSSF 202.

3GPP technical specification 29.531 section 5.3.2.3 explains thesubscribe operation used by a NF Service Consumer (e.g., AMF) tosubscribe to a notification of any changes in status of the NSSAIavailability information (e.g. S-NSSAIs available per TA and therestricted S-NSSAI(s) per PLMN in that TA in the serving PLMN of the UE)upon this is updated by another AMF. In brief, the subscription is foran AMF to get updates from NSSF 202 on NSSAI availability informationduring modification. The modification of NSSAI Availability can beeither be through other AMFs or operator configuration at NSSF 202.

3GPP technical specification 29.510 section 5.3.2.5 explains that thenotify service operation shall be used by NSSF 202 to update the NFService Consumer (e.g., AMF) with any change in status, on a per TAbasis, of the S-NSSAIs available per TA (unrestricted) and the S-NSSAIsrestricted per PLMN in that TA in the serving PLMN of the UE. In brief,NSSF 202 shall trigger a notification to all of the subscribed AMFs uponany NSSAI availability information update at NSSF 202. This can be dueto other AMFs update on NSSAI Availability information or throughoperator configuration.

In response to NSSF 202 going out of service (for example due to anapplication crash, NSSF overload, DB connectivity issues or any othersimilar situations where NSSF 202 is unable to process the incomingNSSAI availability update requests from AMFs 204, 206, and 208), therecould be multiple updates that will be missed to be applied to thepersistent data on NSSAI availability information. The missed updatescould result in missed triggering of the notifications to all thesubscribed AMFs on the updated NSSAI availability information.

When NSSF recovers from the failures, then there will be discrepancybetween the NSSAI availability information:

-   -   among different AMFs, e.g., between an AMF that updated the        NSSAI availability information and an AMF that is expecting the        update notification by virtue of the subscription.    -   between AMFs and NSSF 202, because NSSF 202 could not process        the incoming NSSAI availability information update request.

FIG. 3 is a ladder diagram illustrating an exchange of messages 300between an example NSSF 202, a first AMF 204, and a second AMF 206.

AMF 204 sends a NSSAI availability PUT (create) request message 302 toNSSF 202. NSSF 202 stores the NSSAI availability informationpersistently in the local storage. NSSF 202 sends a success responsemessage 304.

AMF 204 sends a subscribe request message 306 to NSSF 202 and therebysubscribes for NSSAI availability information updates from NSSF 202.NSSF 202 creates the subscription, for example, by storing an identifierfor AMF 204 in a list of subscribed AMFs, and sends a success responsemessage 308 to AMF 204.

AMF 206 sends a subscribe request message 310 to NSSF 202 and therebysubscribes for NSSAI availability information updates from NSSF 202.NSSF 202 creates the subscription, for example, by storing an identifierfor AMF 206 in a list of subscribed AMFs, and sends a success responsemessage 312 to AMF 204.

At 314, NSSF 202 becomes unavailable, for example, NSSF 202 crashes orbegins shedding traffic due to being overloaded. AMF 204 sends a NSSAIavailability PATCH (update) request message 316; however, NSSF 202 isunable to receive or process this message.

At 318, NSSF 202 recovers and becomes available again, for example, bycompleting a reboot or by exiting an overloaded state. Due to the missedmessage 316, there is discrepant NSSAI availability information acrossthe network functions.

AMF 204 includes updated availability data 320, and AMF 204 attempted toupdate NSSF 202 with message 306 but failed due to NSSF 202 beingunavailable. AMF 206 includes stale availability data 322 since it didnot receive an update from NSSF 202. NSSF 202 includes staleavailability data 324 since it was unable to receive or process message306.

To avoid stale availability data 322 and 324, NSSF 202 can be configuredsuch that, upon NSSF recovery from any failure scenarios, NSSF 202 cantrigger a notification request towards subscribed AMFs. In thenotification request, NSSF 202 includes a new optional indication. Uponreceiving the notification trigger with optional indication, an AMF cantrigger an NSSAI availability request towards NSSF 202 with the updatedNSSAI availability information. NSSF 202 can then process the request byupdating the storage and trigger a notification to all the subscribedAMFs.

In some examples, in response to NSSF 202 failing to process an incomingrequest due to unavailability, NSSF 202 is configured to:

-   -   trigger a notification request towards subscribed AMFs    -   during NssfEventNotification message, NSSF 202 includes an        indication of “NSSAIAvailabilityUpdateRequired” (or any other        appropriate indication) in the form of header or data attribute

This is to inform subscribed AMFs that NSSF 202 does not have the latestNSSAI availability information and is now requesting the latestinformation. AMFs 204 and 206 are configured to process the notificationrequest with the indication as below:

-   -   Upon receiving “NSSAIAvailabilityUpdateRequired” header/data        attribute, trigger the NSSAI availability update request towards        NSSF with the updated NSSAI Availability information

NssfEventNotification is defined in 3GPP technical specification 29.531section 6.2.6.2.10.

FIG. 4 is a table illustrating example attribute names and values for anotification message 400. Notification message 400 includes an attributename/header called “NSSAIAvailabilityUpdateRequired” having a data type“Boolean” and cardinality of 1. The attribute is an indication for anAMF to resend NSSAI availability information.

FIG. 5 is a ladder diagram showing an example exchange of messages 500between an example NSSF 202, a first AMF 204, and a second AMF 206. Asshown in FIG. 5 , NSSF 202 is configured for NSSF recovery using thetrigger notification described above. Prior to the exchange 500 shown inFIG. 5 , AMF 204 has already subscribed to NSSF 202 for NSSAIavailability updates.

AMF 204 sends an availability PUT request message 502 to NSSF 202. NSSF202 stores the availability data persistently in a database. NSSF 202sends a success response message 504.

AMF 206 sends a subscribe request message 506 to NSSF 202 and therebysubscribes for NSSAI availability information updates from NSSF 202.NSSF 202 creates the subscription, for example, by storing an identifierfor AMF 206 in a list of subscribed AMFs, and sends a success responsemessage 508 to AMF 204.

At 510, NSSF 202 becomes unavailable, for example, NSSF 202 crashes orbegins shedding traffic due to being overloaded. AMF 204 sends a NSSAIavailability PATCH (update) request message 512; however, NSSF 202 isunable to receive or process this message. At 514, NSSF 202 recovers andbecomes available again, for example, by completing a reboot or byexiting an overloaded state.

NSSF 202 triggers a notify request message 516, to each of AMFs 204 and206, with the update request indication, e.g.,“NSSAIAvailabilityUpdateRequired.” AMFs 204 and 206 respond with asuccess response message 518.

AMF 204 processes the notify request message 516 and triggers the NSSAIavailability towards NSSF 202 with updated NSSAI availabilityinformation by sending another availability PATCH (update) requestmessage 520. NSSF 202 updates the latest NSSAI availability information.NSSF 202 sends a success response message 522 to AMF 204.

NSSF 202 triggers the notification to the subscribed AMFs. In this case,NSSF 202 does not need to send a notification to AMF 204 since AMF 204provided the update. NSSF 202 sends a notify request message 524 to AMF206. AMF 206 responds with a success response message 526.

As a result, each of AMF 204, AMF 206, and NSSF 202 has synchronizedNSSAI availability data. AMF 204 has updated availability data 528, AMF206 has updated availability data 530, and NSSF 202 has updatedavailability data 532.

FIG. 6 is a flow diagram of an example method 600 for NSSF recovery.Method 600 can be performed by one or more NSSFs in a telecommunicationsnetwork.

Method 600 includes creating, at an NSSF, subscriptions for a number ofaccess and mobility management functions (AMFs) and storing availabilityinformation for each AMF (602). The availability information can be,e.g. network slice selection assistance information (NSSAI). Creatingthe subscriptions can include, e.g., receiving a subscribe serviceoperation request message from each AMF. Storing availabilityinformation for each AMF can include receiving a NSSAI availability PUTrequest from each AMF.

Method 600 includes, after creating the subscriptions, receiving anetwork slice selection assistance information (NSSAI) availabilityPATCH request from at least one AMF and storing new availabilityinformation for the at least one AMF (604). Method 600 can include,after creating the subscriptions, receiving a network slice selectionassistance information (NSSAI) availability update resulting from atelecommunications network operator configuration.

Method 600 includes distributing the NSSAI availability update (from thePATCH request or the operator configuration) to each of the subscribedAMFs (606).

Method 600 includes determining, at the NSSF, that the NSSF failed toprocess at least one service update message from at least one of theAMFs, and in response, sending a notification request message to each ofthe AMFs (608). The notification request message includes datarequesting each AMF to update availability information for the AMF.Sending the notification request message to each of the AMFs includes,in some examples, including data requesting updated availabilityinformation in the form of a header or data attribute of a notifyservice operation message.

Determining that the NSSF failed to process a service update messagegenerally includes determining that the NSSF experience an outage. Forexample, determining that the NSSF failed to process at least oneservice update message can include determining that the NSSF implementeda traffic shedding policy in response to detecting an overloadcondition. As another example, determining that the NSSF failed toprocess at least one service update message can include determining thatthe NSSF was unavailable for a period of time.

Method 600 includes receiving, at the NSSF, updated availabilityinformation from each of the AMFs (610) and storing the updatedavailability information. Method 600 includes distributing, at the NSSF,the updated availability information to each of the AMFs (612).

REFERENCES

The disclosure of each of the following references is incorporatedherein by reference in its entirety.

-   1. 3^(rd) Generation Partnership Project; Technical Specification    Group Core Network and Terminals; 5G System; Network Function    Repository Services; Stage 3 (Release 17) 3GPP TS 29.510 V17.3.0    (2021 September)-   2. 3^(rd) Generation Partnership Project; Technical Specification    Group Core Network and Terminals; 5G System; Network Slice Selection    Services; Stage 3 3GPP TS 29.531 V16.3.0 (2020 July)

The scope of the present disclosure includes any feature or combinationof features disclosed in this specification (either explicitly orimplicitly), or any generalization of features disclosed, whether or notsuch features or generalizations mitigate any or all of the problemsdescribed in this specification. Accordingly, new claims may beformulated during prosecution of this application (or an applicationclaiming priority to this application) to any such combination offeatures.

In particular, with reference to the appended claims, features fromdependent claims may be combined with those of the independent claimsand features from respective independent claims may be combined in anyappropriate manner and not merely in the specific combinationsenumerated in the appended claims.

What is claimed is:
 1. A method for network slice selection function(NSSF) recovery, the method comprising: creating, at an NSSF, aplurality of subscriptions for a plurality of access and mobilitymanagement functions (AMFs) and storing availability information foreach AMF; determining, at the NSSF, that the NSSF failed to process atleast one service update message from at least one of the AMFs, and inresponse, sending a notification request message to each of the AMFs,the notification request message requesting each AMF to updateavailability information for the AMF; receiving, at the NSSF, updatedavailability information from each of the AMFs; and distributing, at theNSSF, the updated availability information to each of the AMFs.
 2. Themethod of claim 1, wherein the availability information comprisesnetwork slice selection assistance information.
 3. The method of claim1, wherein determining that the NSSF failed to process at least oneservice update message comprises determining that the NSSF implemented atraffic shedding policy in response to detecting an overload condition.4. The method of claim 1, wherein determining that the NSSF failed toprocess at least one service update message comprises determining thatthe NSSF was unavailable for a period of time.
 5. The method of claim 1,wherein creating the plurality of subscriptions comprises receiving asubscribe service operation request message from each AMF.
 6. The methodof claim 1, wherein storing availability information for each AMFcomprises receiving a network slice selection assistance information(NSSAI) availability PUT request from each AMF.
 7. The method of claim1, comprising, after creating the plurality of subscriptions, receivinga network slice selection assistance information (NSSAI) availabilityPATCH request from at least one AMF and storing new availabilityinformation for the at least one AMF.
 8. The method of claim 1,comprising, after creating the plurality of subscriptions, receiving anetwork slice selection assistance information (NSSAI) availabilityupdate resulting from a telecommunications network operatorconfiguration.
 9. The method of claim 8, comprising distributing theNSSAI availability update to each of the AMFs.
 10. The method of claim1, wherein sending the notification request message to each of the AMFscomprises including data requesting updated availability information inthe form of a header or data attribute of a notify service operationmessage.
 11. A system for network slice selection function (NSSF)recovery, the system comprising: at least one processor and memorystoring instructions for the at least one processor; a NSSF implementedby the at least one processor and configured for: creating a pluralityof subscriptions for a plurality of access and mobility managementfunctions (AMFs) and storing availability information for each AMF;determining that the NSSF failed to process at least one service updatemessage from at least one of the AMFs, and in response, sending anotification request message to each of the AMFs, the notificationrequest message requesting each AMF to update availability informationfor the AMF; receiving updated availability information from each of theAMFs; and distributing the updated availability information to each ofthe AMFs.
 12. The system of claim 11, wherein the availabilityinformation comprises network slice selection assistance information(NSSAI).
 13. The system of claim 11, wherein determining that the NSSFfailed to process at least one service update message comprisesdetermining that the NSSF implemented a traffic shedding policy inresponse to detecting an overload condition.
 14. The system of claim 11,wherein determining that the NSSF failed to process at least one serviceupdate message comprises determining that the NSSF was unavailable for aperiod of time.
 15. The system of claim 11, wherein creating theplurality of subscriptions comprises receiving a subscribe serviceoperation request message from each AMF.
 16. The system of claim 11,wherein storing availability information for each AMF comprisesreceiving a network slice selection assistance information (NSSAI)availability PUT request from each AMF.
 17. The system of claim 11,wherein the NSSF is configured for, after creating the plurality ofsubscriptions, receiving a network slice selection assistanceinformation (NSSAI) availability PATCH request from at least one AMF andstoring new availability information for the at least one AMF.
 18. Thesystem of claim 11, wherein the NSSF is configured for, after creatingthe plurality of subscriptions, receiving a network slice selectionassistance information (NSSAI) availability update resulting from atelecommunications network operator configuration and distributing theNSSAI availability update to each of the AMFs.
 19. The system of claim11, wherein sending the notification request message to each of the AMFscomprises including data requesting updated availability information inthe form of a header or data attribute of a notify service operationmessage.
 20. One or more non-transitory computer readable media havingstored thereon executable instructions that when executed by at leastone processor of a computer cause the computer to perform stepscomprising: creating, at an NSSF, a plurality of subscriptions for aplurality of access and mobility management functions (AMFs) and storingavailability information for each AMF; determining, at the NSSF, thatthe NSSF failed to process at least one service update message from atleast one of the AMFs, and in response, sending a notification requestmessage to each of the AMFs, the notification request message requestingeach AMF to update availability information for the AMF; receiving, atthe NSSF, updated availability information from each of the AMFs; anddistributing, at the NSSF, the updated availability information to eachof the AMFs.